The present invention relates to an image transforming device such as a frame synchronizer,
Conventionally, image transforming devices such as frame synchronizers have employed a variety of means to transform video signal formats, For example, Japanese Laid-Open No, 62-186683 proposes a method in which some of the image data are deleted or repeated frame by frame. Such a method easily changes frame frequencies.
On the other hand, Japanese Laid-Open No. 62-35788 proposes a method for changing frame frequencies in which image data of a frame are formed from data of the preceding and subsequent frames by using a linear interpolation technique. Another method may be considered in which frame-interpolation is performed, instead of using the linear interpolation technique, according to a time function expressing change in image data, the time function being detected in each panel.
In such ways, the above methods form video signals which produce smooth motions by and large, compared with methods in which image data is partially detected simply frame by frame.
These conventional image transforming methods have a problem in that when an image containing a moving portion is transformed, degradation of image quality is inevitable. To solve that problem, Japanese Laid-Open No. 62-25587 proposes a method in which frame-interpolation is performed using a method for detecting motions.
In this method, a moving image portion is extracted from a video signal and only the image data from that portion is formed, while a still image portion is simply taken from the preceding or subsequent frame. In this method, however, it is necessary that the suitable algorithm, i.e., the algorithm for either motion detection or frame-interpolation, be selected according to an image.
Therefore, the described method has a problem in that a transformed image appears unnatural in a case where an entire frame being slowly panned has a portion with an isolated motion unrelated to the panning movement, such as a football moving across a panned frame.